The present invention relates to metal chill plates which are implanted in a mold or flask and a stacked flask assembly using the metal chill plates.
There is a wide range of application for composite materials having a chilled structure which is obtained by rapidly cooling a molten metal poured into a mold or flask having metal chill plates.
In industrial application, these composite materials are typically utilized for making automotive type engine cam shafts and similar types of engine parts in a manner that the cam shafts are cast within the mold in which the chill plates are located to produce hardened surface areas at pre-selected locations on the cam shafts.
Actually, in Japan and Europe, more than 70% of medium and small internal combustion engines excluding those for large ships use the cam shafts made of cast iron having chilled surface areas formed on cam or lobe portions. By chilling the entire circumferences of cam or lobe portions the hardness of the chilled portions and the micro-structures thereof can be further improved, thus, the application of such materials is increased.
Systems for casting the chilled cam shafts currently produced in Japan and Europe are generally classified into (1) casting using a green sand high pressure mold obtained by mechanical ramming and (2) casting using a mold hardened by using a chemical binder. In either case, a mold structure is employed in which the chill plates are implanted in the mold to forcibly cool and harden cam or lobe portions concurrently with casting. In the United States, the cam shafts are hardened by quenching because such automated implantation of the chill plates in the casting mold is not available.
The recent trend toward automobiles of higher performance has resulted in more complicated valve mechanisms, and this necessitates increasing the number of cams disposed within a predetermined length of the cam shaft and making the surfaces of the increased number of cams harder. For this reason, casting methods utilizing chill plates are attracting more attention.
Referring to casting process by implanting the chill plates in the mold, the green sand high pressure casting wherein water and green sand added with a binder are simply mechanically rammed has been found unsatisfactory in that it is limited in adaptability to product designs intended for the increased number of cams and in that water included in green sand reacts with poured molten metal in contact with the chill plates resulting in accidental internal gas defects which increase in proportion as the number of cams increases.
For the above reasons, the casting using the chemically hardened mold which easily accommodates to near net shapes and has high adaptability to product designs is more advantageous than the casting using the green sand high pressure mold, although the latter provides high productivity. Under such circumstances, most Japanese and European firms producing the chilled cam shafts employ casting based on a shell mold process or cold box process utilizing a chemically hardened mold, and only a limited number of firms employ casting using the green sand high pressure mold for items in limited design shapes.
The chemically hardened molds for the chilled cam shafts for the internal combustion engines of automobiles are produced using the shell mold process wherein upper and lower molds (cope and drag frames) are independently made and are aligned and bonded after manually implanting the chill plates therein. Gating systems used in this case include those to obtain horizontally poured and laterally arranged plural shots, vertically poured and laterally arranged multiple shots, vertically poured and longitudinally arranged plural shots, and vertically poured stack-cast laterally arranged multiple shots.
In the prior art as described above, the stack-cast laterally arranged system is preferred to any other system for casting of the cam shafts from the viewpoint of chill hardness, hardness of shafts, ease of forming hollow shafts, yield in terms of weight, productivity in molding, and productivity in pouring. However, this system has problems to be solved in the aspects of bending of shafts, casting defects, and automated implantation of chill plates and is to be improved further for a better sand-metal ratio. Especially, the sand-metal ratio makes it difficult to form a more compact stacked mold.
It is therefore an object of the present invention to solve the above problems and points to be improved.